Note: Descriptions are shown in the official language in which they were submitted.
CA 02709641 2010-06-16
Binder for Materials Eased on Wood Chips and/or Wood Fibers,
Method for the Production Thereof, and Molded Article
The invention relates to a binder for producing materials based on wood chips
and/or wood fibers, the binder according to the invention being used for
produc-
ing and gluing e.g. wood dust-type, wood chip-type, wood veneer-type, solid
wood-type materials and/or materials based on fibers, such as wood and/or
plant
fibers, e.g. annual and perennial plants.
The material thus produced is a board, mat or a molded article produced from
wood and/or fiber particles of any geometry and consistency, such as a chip-
board, a plywood panel, a solid wood board, a board based on chip-type materi-
als such as OSB (oriented strand board), laminated strand board (LSL) or a
board based on veneers, such as LVL (laminated veneer lumber), or plywood.
Other possible wood materials are fiber boards, fiber mats, such as an
insulating
fiber mat, as well as molded articles produced therefrom, or combinations of
the
individual materials, although the above-mentioned items do not represent a
rating description of possible uses of the binder according to the invention.
The binders currently used for producing such materials are almost exclusively
synthetic binders.
Quantitatively, by far the most significant part, namely about 6 million
tons/year
(estimated as a liquid form of supply) in Europe, involves formaldehyde-based
condensation resins such as urea-formaldehyde (UF), melamine-formaldehyde
(MF), melamine-urea-formaldehyde (MUF), melamine-urea-phenol-formaldehyde
(MUPF), phenol-formaldehyde (PF), phenol-melamine-formaldehyde (PMF),
phenol-urea-formaldehyde (PUF), resorcinol-phenol-formaldehyde (RPF), resor-
cinol-phenol-urea-formaldehyde (RPUF) or mixtures thereof.
Also, but to a much lesser extent, adhesives from the group of polyurethanes
and so-called polymeric diphenylmethane diisocyanates (PMDI) as well as ther-
moplastic binders, such as those based on polyolefins, polyvinyl chloride,
ther-
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moplastic bonding fibers, polyvinyl acetates or polyvinyl alcohols, are being
used.
More specifically, synthetic binders are advantageous in that, by way of
selecting
the latter, targeted influence on the properties of the materials produced
there-
from is possible and their production can be made highly effective, and that
property-related insensitivity to the basic chemical raw materials is
existing, es-
pecially in terms of time or seasonal conditions.
One apparent drawback is that the starting materials required to produce the
synthetic binders are ultimately based on petroleum/natural gas or carbon chem-
istries. These resources are limited and subject to major fluctuations in
price and
availability as a result of economic and socio-political developments in
recent
years and the ongoing globalization. The increase in prices observed over pro-
longed periods will tend to continue as a result of the worldwide ever-
increasing
consumption of oil, gas and coal and a possible shortage of resources.
From an ecological view and with respect to long-term, sustainable resource
economy, careful treatment of these irretrievably limited resources and search
for alternatives therefore should be given top priority. In recent years,
attempts
have therefore been made to increasingly redevelop, market and use natural
animal- and vegetable-based binders.
Such binders on a natural basis have been known since antiquity and used over
the centuries. In this context, glues and adhesives based on animal connective
tissue, such as glutin glue, based on milk proteins, such as casein glues, or
based on water-soluble proteins, such as blood albumin glues, should be men-
tioned as examples.
For many years, there has been work on improved, alternative, natural binders,
e.g. based on polyphenolic wood constituents such as tannins, binders based on
various lignin variants, binders based on vegetable proteins, such as soybeans
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and wheat, or based on starch and sugars, just to name a few examples, without
claiming completeness of the above-mentioned items. There is extensive
literature relating to such activities, e.g. M. Dunky and P. Niemz:
Holzwerkstoffe
and Leime; Technologie and EinflufMaktoren, Springer-Verlag Heidelberg, 2002.
Despite all efforts, natural binding agents still involve significant
drawbacks resid-
ing, in particular, in the processing characteristics, technological
parameters of
use, achievable properties of the materials produced therefrom, as well as in
the
entire cost structure.
Thus, in particular, the press times used in industrial manufacturing of
boards
are still well above those when using synthetic binders. Similarly, most of
the
natural components are not obtained with a defined composition, thus signifi-
cantly impeding their use and the reproducibility of characteristic values
achiev-
able with these products for materials produced therefrom.
It is therefore much more promising to combine natural and synthetic binders.
Thus, wheat and rye flours have been used for decades in glue baths for ply-
wood production both as extenders and to increase the cold tack of glues used.
Although limited in use, natural binders and products are now firmly
established
as fillers and extenders for synthetic glues. However, when using such fillers
and
extenders based on natural raw materials, it must be assumed in most cases
that there will be no effective chemical incorporation or binding to the
synthetic
binder to form chemical primary bonds. Only mechanical fixing in the cured net-
work of the synthetic binder or partial binding via secondary valences is
conceiv-
able.
It would therefore make much more sense to actively incorporate such natural
binders or products in synthetic binder systems to form direct chemical bonds.
This would imply that the substances used, based on natural raw materials, not
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only serve as rather inactive fillers and extenders, but make a direct
contribution
as an active binding agent.
This would also provide important labor market stimuli by creating more jobs
in
agriculture, save resources and minimize the use of substances considered
criti-
cal in ecological terms, such as formaldehyde.
Emissions of formaldehyde from finished materials and products such as those
mentioned above as examples of various wood materials can be reduced to very
low values as a result of the sufficiently well known formaldehyde-binding
effect
of proteins. Some natural substances such as wood materials are known to con-
tain naturally formed formaldehyde, as has been described in detail in the
litera-
ture (e.g. B. Meyer and C. Bohme, Holz- and Kunststoffverarb. 29 (1994) 1258 -
1259; or Holz Zentr. BI. 120 (1994) 1969 - 1972; or Holz Roh. Werkst. 53
(1995)
135).
Suitable substances based on natural renewable raw materials can be very dif-
ferent in their chemical nature. Tannins and lignins of varying origin are
based on
the basic structures of phenol and phenol derivatives; proteins, depending on
their origin, are constituted of various amino acids, while other possible sub-
stances are based on starch and sugars/carbohydrates. In particular, proteins
based on vegetable raw materials have been investigated in more detail in re-
cent years and represent promising compounds for specific uses and direct
chemical incorporation in various synthetic binders. Thus, significant improve-
ments have been achieved in recent years by condensation of vegetable protein
components into e.g. phenolic resins.
Comprehensive results of this work have been described in EP 1318000.
Therein, the amino groups of the proteins are reacted with formaldehyde and
crosslinked with the methylol groups of the phenolic resin.
However, apart from the great improvements achieved in the properties of the
basic synthetic binders, there is still the disadvantage that, due to their
relatively
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high molecular weights, vegetable-based protein components previously used
have a poorly suitable, relatively high viscosity of more than 600 mPas at 20
C in
liquid form.
The majority of condensation resins, especially UF, MUF and MUPF resins, are
used with a resin content of about 65% so that excess water introduced into
the
glue system via these natural components must be removed with high input of
time and energy, which also limits the potential of incorporation by
condensation
and the thus achievable product properties of materials produced using these
binders. As a result of massive vapor formation, high water contents in the
bind-
ers being used give rise to technological problems when manufacturing various
materials such as boards of different shape and, as a consequence, instability
of
the boards produced. Another drawback is delayed chemical formation due to
shifts of - usually achievable - chemical equilibria away from the cured
structures
and towards the chemical starting materials.
A wider use of substances and materials based on natural raw materials for the
production of binders, regardless whether a pure binder based on these natural
raw materials or mixtures or reaction mixtures including various synthetic
binders
and binder components are concerned, is still opposed by a number of problems
and prejudices. In general, the manufacturing costs of such natural or
partially
natural binders are considerably higher than those of synthetic binders; also,
there are still controversial opinions regarding various parameters such as
toxic-
ity and biodegradability. As for many types of natural binders, a satisfactory
level
of technology with respect to the properties of the binders and the use and
prop-
erties of products produced therefrom has not been achieved as yet. Also,
there
are still great regional differences with respect to production, properties
and use
of such natural binders to some extent. Moreover, it is necessary in some
cases
to prove continuous and qualitatively constant supply of the market with
natural
binders, particularly with respect to geographical and climatic conditions or
exist-
ing harvesting conditions.
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Also, some binders or binder components based on natural raw materials fre-
quently involve the drawback of lower reactivity compared to various synthetic
binders, which is due to the lower number of reactive sites in the molecule
and a
more complex chemical structure, and consequent slower curing. The lower
number of reactive groups and reactive sites also produces a lower degree of
crosslinking and, as a consequence, lower crosslinking density, which may
result
in inferior mechanical and physical properties, such as lower strength.
The object of the invention is therefore to provide a binder for producing and
glu-
ing materials based on wood chips and/or wood fibers, which binder contains
natural protein components and significantly reduces or even avoids the disad-
vantages of the prior art and, in addition, can be produced and used economi-
cally.
More specifically, this relates to a binder which should be variable in its
viscosity
within wide limits without requiring adjustment of excessively high water con-
tents. Moreover, the protein component in the binder should have high
reactivity
so as to be capable of achieving high crosslinking density.
Said object is accomplished by means of a binder for materials based on wood
chips and/or wood fibers, comprising an aldehyde-based condensation resin and
further additives, which is characterized in that it has a water-soluble
reactive
additive including a peptide/amino acid mixture without a proportion of water-
insoluble, highly viscous proteins such as collagen, wherein "without a propor-
tion" is understood to imply "without a significant proportion". Major
proportions
of such proteins will adversely affect the water solubility and viscosity of
the re-
active additive. Water-soluble is understood to imply that at least 94% of the
re-
active additive will dissolve in water at a temperature of 20 C. Most
frequently,
the water solubility is even close to 100%.
The method for producing the binder is characterized in that the reactive
additive
is incorporated in the aldehyde-based condensation resin by chemical conden-
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sation during resin production and/or added following resin production and/or
immediately prior to processing the binder by grinding or mixing in liquid
phase
or by means of other suitable mixing procedures.
Using the binder according to the invention, it is possible to produce molded
arti-
cles based on wood chips and/or wood fibers.
Advantageous developments of the binder are set forth in the subclaims.
In an advantageous development of the binder, the peptides and amino acids in
the peptide/amino acid mixture are present in a mass ratio of from 0.1 : 1 to
10: 1.
Another embodiment of the binder according to the invention is characterized
in
that the reactive additive has a molecular weight distribution of about 90% of
the
total amount between 0.13 to 50 kilodaltons (kDa) at an average molecular
weight of 1 to 20 kDa.
In an advantageous embodiment of the binder, the reactive additive has a reac-
tive amino nitrogen content of from 0.7 to 5%, based on the dry mass.
It is envisaged in a further embodiment that the reactive additive is produced
by
means of high-pressure thermolysis of proteinaceous animal raw materials in an
aqueous medium, which is performed in two stages, wherein in a first stage a
temperature of from 140 to 190 C and a pressure of from 10 to 50 bar is ad-
justed at a hold time of from 5 to 60 min, and in a second stage a target tem-
perature of from 180 to 230 C and a pressure of from 20 to 100 bar is adjusted
at a hold time of from 1 to 30 min, said hold time decreasing from stage to
stage.
In one embodiment of the binder the aldehyde is formaldehyde.
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Another embodiment of the binder is characterized in that the formaldehyde-
based condensation resin preferably consists of the group of urea-formaldehyde
(UF), melamine-formaldehyde (MF), melamine-urea-formaldehyde (MUF),
melamine-urea-phenol-formaldehyde (MUPF), phenol-formaldehyde (PF), phe-
nol-melamine-formaldehyde (PMF), phenol-urea-formaldehyde (PUF), resorci-
nol-phenol-formaldehyde (RPF), resorcinol-phenol-urea-formaldehyde (RPUF)
and/or mixtures thereof.
In one development the binder includes 1 to 60% by weight reactive additive.
In one embodiment the binder includes 2 to 50% by weight reactive additive.
One development is characterized in that the binder includes 5 to 40% by
weight
reactive additive.
One inventive embodiment of the binder is characterized in that hydrophobizing
agents, flame retardants and/or fungicides, bactericides, dyes, pigments, odor
inhibitors, conductivity-increasing substances, viscosity-increasing
additives, as
well as fillers or extenders are included as further additives.
In another embodiment the binder includes thermoplastics such as polyolefins,
polyvinyl chloride, bonding fibers, polyvinyl acetate and/or additives based
on
proteins, lignins, tannins, polysaccharides such as starch, and/or
polyurethanes
as well as polymeric diisocyanates such as polymeric diphenylmethane diisocy-
anates and mixtures thereof as further additives.
Advantageously, it was found that the reactive additives used can be incorpo-
rated preferably by condensation in the appropriate binder from the group of
condensation resins based on aldehydes, particularly formaldehyde, during the
binder production process. One essential part of the technology described
herein
is that the reactive additive is chemically incorporated via its large number
of re-
active groups in the synthetic binder during the preparation thereof, or, in
the
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event of adding the peptide/amino acid mixture to the finished synthetic resin
and/or immediately prior to processing the synthetic resin during chemical
curing
of the synthetic resin via its reactive groups, reacts with the synthetic
resin to be
chemically incorporated.
In a particularly preferred embodiment, the ratio of included peptides and
amino
acids with a molecular weight of less than 10 kDa should be 80% and in a
highly
preferred embodiment more than 90%.
The mass-related shares of all components make 100% in total.
The reactive additive can be used both as an aqueous solution and in spray-
dried form.
Spray drying offers the essential advantage that the peptide/amino acid
mixture
is made extremely stable during storage. It can be used both as an extensively
water-soluble powder during the preparation of the synthetic condensation
resin
and as a powdered additive during grinding and/or other processing of the con-
densation resins based on aldehydes, e.g. formaldehyde, such as novolaks and
solid resols, or in an admixing process with spray-dried synthetic
condensation
products such as UF, MF and PF or other condensation products based on al-
dehydes.
Furthermore, the inventive binder produced using the above-mentioned pep-
tide/amino acid mixture can optionally be added with other natural or
synthetic
components to achieve specific properties (e.g. increase the cold tack, adjust
the
viscosity, etc.). Such addition can be made during the preparation of the
binder
according to the invention, to the finished product binder of the invention,
or im-
mediately prior to or during processing of the binder according to the
invention.
The binder according to the invention and the properties of the materials pro-
duced therefrom, achieved using the binder according to the invention, will be
il-
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lustrated in more detail in the following representations and examples with
refer-
ence to the drawings wherein:
Fig. 1 shows a comparison between a wheat protein (WP1) and the reactive
additive with respect to their molecular weight distribution;
Fig. 2 shows a comparison of the protein or polypeptide content of wheat
protein (WP1) and reactive additive;
Fig. 3 shows a representation of selected material characteristic values of
HDF produced using laboratory technology (hot-stage temperature
220 C, press time factor 15 s/mm);
Fig. 4 shows a representation of selected material characteristic values of
chipboards produced using laboratory technology (hot-stage tempera-
ture 220 C, press time factor 9 s/mm); and
Fig. 5 shows a representation of selected material characteristic values of
chipboards produced using laboratory technology (hot-stage tempera-
ture 220 C, press time factor 15 s/mm).
The advantages of the reactive additive used according to the invention are,
in
particular, that the raw materials are digested to a much higher level so that
the
molecular mass is significantly lower than e.g. that of wheat proteins well-
known
for such uses.
For comparison, the peptide size ratio measured by means of gel permeation
chromatography (GPC) is represented in Fig. 1. WP1 represents wheat protein
glue (Gluvital 21000), a by-product with high value creation potential
obtained in
traditional starch production (wet process). As a rule, this product is in the
form
of a powder and contains -80% (based on dry substance) water-insoluble pro-
teins. Dissolved in an alkaline medium, binders formulated using this product
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were suitable for manufacturing wood material panels with good dry strength,
formaldehyde liberation in the range of native wood, and insufficient moisture
re-
sistance of the glued bond. In addition, the high water contents in WP1 binder
formulations rendered the achievable press times uneconomical (e.g. Krug, D.;
Sirch, H.-J: Protein als Kleber; Anteilige PF-Harz-Substitution moglich. Holz-
Zent.bl. 125 (1999), 773).
The molecular weight distributions were determined on a Pharmacia system with
a column having a length of 60 cm, a diameter of 1.6 cm and a volume of
60.3 ml. The detection was performed at 280 nm. The column material Seph-
adex G-100 (separation range: 1 to 150 kDa) was used as stationary phase.
PBS buffer was used as mobile phase. Gel chromatography standards from Bio-
rad were used as calibration substances to determine the molecule sizes.
The two products also differ significantly both in the soluble components and
in
the protein content/polypeptide content (Fig. 2).
In spray-dried condition the reactive additive is 100% redissolvable in water,
and
no additional water is introduced when using spray-dried products.
Example 1
Preparation of binders
(i) Synthetic resin starting material
Phenolic resins for the wood material industry are being produced using an ex-
cess of formaldehyde versus phenol, i.e. more than I mol of formaldehyde per
mol of phenol. Typically, the molar ratio of phenol to formaldehyde is around
1 :
2.3 to 2.4.
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To demonstrate the advantages of the binder according to the invention, a
molar
ratio of phenol to formaldehyde of 1 : 2.8 was selected each time for the
binders
used in Example 1.
(i) was produced with no reactive additive.
For comparison, a mixture of (i) with the reactive additive, (ii), was tested.
The reactive additive was incorporated by condensation in the inventive binder
(iii) during production so that, based on solid resin of the binder (iii),
about 22%
of the reactive additive are included in solid form.
The synthetic resin starting material (i) and the binder according to the
invention
(iii) are characterized by the following characteristic values:
Characteristic value (i) (iii)
Viscosity at 20 C 110 mPas 468 mPas
Resin content 55.9% 48.6%
H value 9.1 11.8
Gelling time at 100 C 21' 20" 28' 30"
B time at 150 C 47" 60"
Results of board production
Production of HDF boards with PF peptide binder
As binders, (i) a synthetic resin starting material, (ii) a mixture of the
synthetic
resin starting material and a peptide/amino acid mixture (reactive additive),
and
(iii) a resin were used, which was prepared at a molar ratio analogous to (i)
by
incorporating ANiPEPT FF-M by condensation. The comparative tests were per-
formed at a comparable order of magnitude of binder used (Fig. 3).
As evident from the example, the inventive combination achieves quite compa-
rable mechanical properties of the boards thus produced.
Conspicuously and surprisingly, there is a very agreeable side effect
demonstrat-
ing the highly improved incorporation of natural structures in the overall
binder
compared to the prior art.
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As a result of the high molar ratio, an above-average perforator value was de-
termined in the PF base resin.
Specifically when incorporating by condensation the peptide/amino acid mixture
(reactive additive) in a PF base resin of equal phenol/formaldehyde molar
ratio,
the significant improvements in subsequent liberation of formaldehyde as a re-
sult of almost complete incorporation of the entire formaldehyde present in
the
binder system in the cured resin structure become apparent, so that the formal-
dehyde emission potential can be reduced by orders of magnitude.
Example 2
Production of chipboards using an UF peptide binder (Fig. 4)
As binders, (iv) a synthetic UF resin with a urea/formaldehyde molar ratio of
from
1 : 1.2, (v) a mixture of the synthetic resin starting material and a
peptide/amino
acid mixture (reactive additive) and (vi) a resin were used, which was
prepared
by incorporating the peptide/amino acid mixture (reactive additive) in the syn-
thetic resin starting material mentioned under (i) by condensation.
Characteristic value (iv) v (vii)
Viscosity at 20 C 277 mPas 641 mPas 362 mPas
Resin content 63.9% 66.6% 65.2%
pH value 9.5 10.0 9.7
Gelling time at 100 C 37" 58" 52"
The comparative tests were performed at a comparable order of magnitude of
binder used.
The transverse tensile strengths of resins modified with the peptide/amino
acid
mixture are lower. They can be improved by using more intense curing (more
powerful or higher amounts of curing agent) or by modifying the process condi-
tions (longer press times and/or higher press temperatures).
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As above in the variants shown in Example 1, subsequent formaldehyde emis-
sion of the board bonded with the resin starting material was likewise reduced
in
Example 2, especially when using the inventive binder produced by
incorporation
of the peptide/amino acid mixture (reactive additive) in the resin starting
material
by condensation, which is illustrated by comparing the perforator values meas-
ured on these panels according to EN 120.
Example 3
Use of the peptide/amino acid mixture (reactive additive) with no synthetic
binder
component in wood material production (Fig. 5)
While testable boards are obtained when using no synthetic binder component
(extended press times, not optimized), the strengths, however, are very low.
What is remarkable are the low formaldehyde contents measured as perforator
value, which are in the range of native wood.
